started work on e-RK-4 for outflux calculation

Ausgleichsbecken.py

@@ -1,6 +1,6 @@
 import numpy as np 
 
-def Volume_trend(influx,outflux,timestep=1,V_0=0):
+def Volume_trend(influx, outflux, timestep=1, V_0=0):
     '''
     Returns the trend and the volume and the final volume,  defined
     by influx and outflux patterns. The optional parameter timestep
@@ -12,7 +12,7 @@ def Volume_trend(influx,outflux,timestep=1,V_0=0):
     V_end = V_trend[-1]
     return V_end,  V_trend
 
-def Height_trend(V_trend,area=1,h_crit_low=-np.inf,h_crit_high=np.inf):
+def Height_trend(V_trend, area=1, h_crit_low=-np.inf, h_crit_high=np.inf):
     '''
     Returns the trend and the height and the final height,  defined
     by influx and outflux patterns as well as the crosssection area.
@@ -24,12 +24,44 @@ def Height_trend(V_trend,area=1,h_crit_low=-np.inf,h_crit_high=np.inf):
     h_crit_flag_low = np.any(h_trend <= h_crit_low)
     h_crit_flag_high = np.any(h_trend >= h_crit_high)
     h_end = h_trend[-1]
-    return h_trend,h_end,h_crit_flag_low,h_crit_flag_high
+    return h_trend, h_end, h_crit_flag_low, h_crit_flag_high
+
+def get_h_halfstep(initial_height, influx, outflux, timestep, area):
+    h0      = initial_height
+    Q_in    = influx
+    Q_out   = outflux
+    dt      = timestep
+    A       = area
+
+    h_halfstep = h0+1/A*(Q_in-Q_out)*dt/2
+
+def get_p_halfstep(p0, p1):
+    p_halfstep = (p0+p1)/2
+
+def FODE_function(x, h, alpha, p, rho=1000, g=9.81):
+    f = x**2/h*alpha+g+p/(rho*h)
+    return f
+
+
+def e_RK_4(yn, h, dt, Q0, Q1, A0, A1, p0, p1):
+    alpha = (A1/A0-1)
+
+    h_hs = get_h_halfstep(h, Q0, Q1, dt, A0)
+    p_hs = get_p_halfstep(p0, p1)
+    Y1 = yn
+    Y2 = yn + dt/2*FODE_function(Y1, h, alpha, p0)
+    Y3 = yn + dt/2*FODE_function(Y2, h_hs, alpha, p_hs)
+    Y4 = yn + dt*FODE_function(Y3, h_hs, alpha, p_hs)
+    ynp1 = yn + dt/6*(FODE_function(Y1, h, alpha, p)+2*FODE_function(Y2, h_hs, alpha, p_hs)+ \
+        2*FODE_function(Y3, h_hs, alpha, p_hs)+ FODE_function(Y4, h, alpha, p))
+
+
+
 
 ## testing
-if __name__ == "__main__":
+# if __name__ == "__main__":
-    influx = np.full([1,100], 6)
+#     influx = np.full([1, 100],  6)
-    outflux = np.full_like(influx, 4)
+#     outflux = np.full_like(influx,  4)
-    V_end, V_trend = Volume_trend(influx, outflux,timestep=0.5,V_0 = 100)
+#     V_end,  V_trend = Volume_trend(influx,  outflux, timestep=0.5, V_0 = 100)
-    print(V_end)
+#     print(V_end)
-    print(V_trend)
+#     print(V_trend)